1. Field of the Invention
The present invention relates to a light emitting device for realizing an optical communication, and an optical communication device including a light emitting device as well as an optical communication system including a light emitting device
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
2. Description of the Related Art
Some of the conventional techniques for realizing the information communication device and system by use of an illumination device have been proposed.
Japanese laid-open patent publication No. 61-202536 discloses an optical communication method and system, wherein the system includes an illumination device and a light-receiving device which detects a light intensity and light spectrum. The light intensity or the quantity of photons emitted from the illumination device is modified in accordance with a transmission signal. A signal device detects the intensity of or the spectrum of the modified light from the illumination device to demodulate the transmission signal. The illumination device has both functions of illumination and transmitter for transmitting data.
Japanese laid-open patent publication No. 62-48139 discloses a data communication device which has a transmission control means for subjecting a predetermined signal to a high frequency modification for transmission onto an electric light line, an illumination device lighting by the electric light line, an optical sensor for receiving the light from the illumination device and detecting a high frequency signal, and a receiving control means for demodulating the high frequency signal.
Japanese laid-open patent publication No. 11-127170 discloses a communication method for data transmission between computers by use of a fluorescent lamp without use of any cable or data transmission line, wherein a power inverter of an illumination device using a fluorescent lump is driven by transmission data so as to realize data transmission depending on an illumination light from the fluorescent lump, so that a computer receives the illumination light for demodulating the modulated signal transmitted on the illumination light and receiving the data.
Japanese laid-open patent publication No. 2001-119338, corresponding to WO96/03811, discloses a power consumption control method and apparatus for a communication system subscriber unit, wherein a subscriber unit of a time division multiple access (TDMA) radiotelephone system is reconfigured in each time slot to a power consumption tessellation.
Japanese laid-open patent publication No. 07-064878, which corresponds to U.S. Pat. No. 5,664,220, discloses an information transmission/reception system which can receive a plurality of transmission requests and transmit information to requesters.
Japanese laid-open patent publication No. 08-274758, which corresponds to U.S. Pat. No. 5,940,769, discloses a radio communication system capable of effectively utilizing the channel by rational transmission of data in radio transmission.
The above-described Japanese laid-open patent publications Nos. 61-202536 and 62-48139 do not disclose the fluorescence. The above-described Japanese laid-open patent publication No. 11-127170 discloses the fluorescent lamp as the light-emitting device.
In order to realize the communication system using the light, it is important how to select the luminescence material because the data transmission speed of the communication system depends on a rising time of in luminance of the luminescence material. In order to realize a high data transmission speed of the communication system, a shortened rising time of the luminance of the luminescence material is essential.
It is no doubt apparent that the fluorescent lamp is unsuitable for realizing a high data transmission speed of the communication system because the rising time of the luminance of the fluorescent lamp is extremely slow, for example, as slow as seconds-order.
Another system for reproducing informations which were stored in an information storage unit has been known, wherein an identification-required object such as goods on a shop is attached with a bar-code pattern which serves as an information storage unit for storing predetermined informations, so that the informations stored in the form of the bar-code pattern as the information storage unit may be reproduced by use of a bar-code reader so as to reproduce the information related to the identification-required object.
The last-described conventional technique using the bar-code pattern is inconvenient because it is necessary for renewing the information to replace the bar-code pattern, which stores the old information into a new bar-code pattern which stores a new information.
The replacement of many informations assigned to many identification-required objects is time-consuming and costly procedure. Overwriting the information, for example, adding the new bar-code pattern to the old bar-code pattern allows any third party including consumer to be aware of the fact that the information on the bar-code pattern was replaced or renewed, and also to know the old informations on the old bar-code pattern. Two or plural bar-code patterns attached onto the identification-required object may cause deterioration in appearance of the identification-required object. In order to avoid these problems, it is, of course, needed to remove the old informations, for example, the old bar-code pattern. This removal process may also take a further longer time and a further cost. In worst case, the removal process may provide any damage to the identification-required object.
In the above circumstances, there is desirable the development of a novel communication system including a new light-emitting device being suitable for realizing a high speed data transmission and also being free from the above problems.